Application of Four Measurement Techniques to Understand Natural Source Zone Depletion Processes at an LNAPL Site     

Poonam R. Kulkarni  Charles J. Newell  David C. King  Lisa J. Molofsky  Sanjay Garg 《Ground Water Monitoring & Remediation》2020,40(3):75-88

There are several key data gaps in our understanding of Natural Source Zone Depletion (NSZD) processes at sites impacted by light nonaqueous phase liquid (LNAPL), and quantifying NSZD rates can be challenging due to the inherent differences in measurement methods. In this study, four different NSZD measurement methods (oxygen influx measured by the Gradient Method, long-term carbon dioxide efflux measured with Carbon Traps, instantaneous carbon dioxide efflux measured with Dynamic Closed Chambers (DCC LI-COR), and the long-term heat flux from biodegradation measured by Thermal NSZD monitoring), as well as LNAPL composition and dissolved gas sampling, were applied at a site in Southern California. These techniques were used to evaluate key questions such as: (1) how do different NSZD rate measurement methods compare, and what causes variability in NSZD results?; (2) to what extent NSZD processes are occurring in LNAPL within the saturated zone?; and (3) how is NSZD related to LNAPL composition change over time? Carbon Traps and Thermal NSZD monitoring measurement methods provided the most consistent NSZD data at this geologically heterogeneous site, with two location average NSZD rates of 540 and 480 gal/acre/year, respectively. Overall, comparisons of NSZD rates between methods were challenging due to different measurement timeframes, significant temporal and spatial heterogeneity, and operational challenges with two of the NSZD methods. Finally, samples of subsurface LNAPL were collected for analysis in 2007 and 2016; results indicated that diesel-range constituents were already very degraded and anaerobic degradation of gasoline-range constituents was ongoing. A LNAPL depletion model (Douglas et al. 1996) applied to the measured LNAPL composition change appeared to greatly overestimate the amount of LNAPL depletion compared to the measured NSZD rate, but did provide an independent semiqualitative line of evidence that LNAPL was being depleted by active NSZD processes at the site.  相似文献   

Overview of Natural Source Zone Depletion: Processes,Controlling Factors,and Composition Change          下载免费PDF全文

Sanjay Garg  Charles J. Newell  Poonam R. Kulkarni  David C. King  David T. Adamson  Maria Irianni Renno  Tom Sale 《Ground Water Monitoring & Remediation》2017,37(3):62-81

Natural source zone depletion (NSZD) has emerged as a practical alternative for restoration of light non‐aqueous phase liquid (LNAPL) sites that are in the later stages of their remediation lifecycle. Due to significant research, the NSZD conceptual model has evolved dramatically in recent years, and methanogenesis is now accepted as a dominant attenuation process (e.g., Lundegard and Johnson 2006 ; Ng et al. 2015 ). Most of the methane is generated within the pore space adjacent to LNAPL (Ng et al. 2015 ) from where it migrates through the unsaturated zone (e.g., Amos and Mayer 2006 ), where it is oxidized. While great progress has been made, there are still some important gaps in our understanding of NSZD. NSZD measurements provide little insight on which constituents are actually degrading; it is unclear which rate‐limiting factors that can be manipulated to increase NSZD rates; and how longevity of the bulk LNAPL and its key constituents can be predicted. Various threads of literature were pursued to shed light on some of the questions listed above. Several processes that may influence NSZD or its measurement were identified: temperature, inhibition from acetate buildup, protozoa predation, presence of electron acceptors, inhibition from volatile hydrocarbons, alkalinity/pH, and the availability of nutrients can all affect methanogenesis rates, while factors such as moisture content and soil type can influence its measurement. The methanogenic process appears to have a sequenced utilization of the constituents or chemical classes present in the LNAPL due to varying thermodynamic feasibility, biodegradability, and effects of inhibition, but the bulk NSZD rate appears to remain quasi‐zero order. A simplified version of the reactive transport model presented by Ng et al. 2015 has the potential to be a useful tool for predicting the longevity of key LNAPL constituents or chemical fractions, and of bulk LNAPL, but more work is needed to obtain key input parameters such as chemical classes and their biodegradation rates and any potential inhibitions.  相似文献   

Impact of Temperature on Groundwater Source Attenuation Rates at Hydrocarbon Sites          下载免费PDF全文

Poonam R. Kulkarni  David C. King  Thomas E. McHugh  David T. Adamson  Charles J. Newell 《Ground Water Monitoring & Remediation》2017,37(3):82-93

The temperature sensitivity of microbial populations is reflected in measured source attenuation rates at hydrocarbon‐impacted sites. The objective of this study was to evaluate the correlation between temperature and source attenuation rates (concentration vs. time attenuation rate over many years) of benzene and toluene by analyzing groundwater monitoring data from >2000 hydrocarbon sites. Historical monitoring records were obtained from three databases, processed to yield long‐term multiyear source attenuation rates, and then compared with representative temperatures at each site. Statistically significant and positive relationships between temperature and source attenuation rates were established for benzene and toluene, indicating that temperature does impact hydrocarbon degradation, but is one of many factors that contribute to source attenuation. There was an observed 1.1 to 1.6 times increase in attenuation rates per 10 °C increase in temperature, which is less than the rate increases predicted by the Arrhenius equation. The temperature dependence on attenuation rate is consistent with several lines of evidence that methanogenesis plays a key role in the rate of hydrocarbon source zone attenuation rather than being controlled strictly by the availability of electron acceptors. First, methanogenesis is known to be strongly influenced by temperature, with significantly higher rates up to about 35 °C. Second, the temperature‐degradation rate relationship was stronger at sites with deeper water tables (>30 ft) that are less susceptible to oxygen influx than sites with shallow water tables (<15 ft). Third, dissolved methane concentrations were higher at sites with warmer temperatures. Overall, these results provide indirect support for a conceptual model where methanogenesis is a key degradation process at hydrocarbon sites, and that attenuation of these source zones is temperature‐sensitive.  相似文献   

Mangrove (Avicennia marina subsp. australasica) litter production and decomposition in a temperate estuary     

RV Gladstone-Gallagher  CJ Lundquist  CA Pilditch 《新西兰海洋与淡水研究杂志》2013,47(1):24-37

Mangrove forests can provide important cross-boundary subsidies of organic matter to adjacent habitats through the production, export, decomposition and assimilation of litter. We quantified two of these components in a temperate mangrove forest in Whangamata Harbour, New Zealand: 1) litter production; and 2) decomposition rates as a function of tidal elevation, sediment type and burial depth. Litter traps sampled monthly for a year measured an annual detrital input of 3.24–5.38 t DW ha^?1, of which 77% occurred in summer. Decomposition rates depended on litter type, with leaves decomposing faster (63 d to decay by 50%) than pneumatophore and wood material (316 and 460 d, respectively). Buried leaf and wood litter decomposed 1.3–1.4 times slower than litter on the sediment surface; however, tidal elevation and sediment type (mud vs. sand) had no effect. The slow decay of litter (an order of magnitude slower than tropical mangrove litter) suggests that its incorporation into temperate marine food webs may be relatively slow.  相似文献   

Snapper (Chrysophrys auratus): a review of life history and key vulnerabilities in New Zealand     

DM Parsons  CJ Sim-Smith  M Cryer  MP Francis  B Hartill  EG Jones 《新西兰海洋与淡水研究杂志》2013,47(2):256-283

Snapper (Chrysophrys auratus) is an important coastal fish species in New Zealand for a variety of reasons, but the large amount of research conducted on snapper has not been reviewed. Here, we review life history information and potential threats for snapper in New Zealand. We present information on snapper life history, defining stages (eggs and larvae, juvenile and adult), and assess potential threats and knowledge gaps. Overall we identify six key points: 1. post-settlement snapper are highly associated with certain estuarine habitats that are under threat from land-based stressors. This may serve as a bottleneck for snapper populations; 2. the largest knowledge gaps relate to the eggs and larvae. Additional knowledge may help to anticipate the effects of climate change, which will likely have the greatest influence on these early life stages; 3. ocean acidification, from land-based sources and from climate change, may be an important threat to larval snapper; 4. a greater understanding of population connectivity would improve certainty around the sustainability of fishery exploitation; 5. the collateral effects of fishing are likely to be relevant to fishery productivity, ecosystem integrity and enduser value; 6. our understanding of the interrelationships between snapper and other ecosystem components is still deficient.  相似文献   

Performance of DNAPL Source Depletion Technologies at 59 Chlorinated Solvent-Impacted Sites   总被引：6，自引：1，他引：5  

Travis M. McGuire  James M. McDade  Charles J. Newell 《Ground Water Monitoring & Remediation》2006,26(1):73-84

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Harold Urey and the moon     

Homer E. Newell 《Earth, Moon, and Planets》1973,7(1-2):1-5

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Ecology of coastal waters: A systems approach: K. H. MannBlackwell Scientific Publications,Oxford, 1982, ix + 322 pp, £25·00 (cloth) £10·80 (paper)     

R.C. Newell 《Estuarine, Coastal and Shelf Science》1983,17(5):589-590

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Results of the first North American comparison of absolute gravimeters, NACAG-2010     

D. Schmerge  O. Francis  J. Henton  D. Ingles  D. Jones  J. Kennedy  K. Krauterbluth  J. Liard  D. Newell  R. Sands  A. Schiel  J. Silliker  D. van Westrum 《Journal of Geodesy》2012,86(8):591-596

The first North American Comparison of absolute gravimeters (NACAG-2010) was hosted by the National Oceanic and Atmospheric Administration at its newly renovated Table Mountain Geophysical Observatory (TMGO) north of Boulder, Colorado, in October 2010. NACAG-2010 and the renovation of TMGO are part of NGS’s GRAV-D project (Gravity for the Redefinition of the American Vertical Datum). Nine absolute gravimeters from three countries participated in the comparison. Before the comparison, the gravimeter operators agreed to a protocol describing the strategy to measure, calculate, and present the results. Nine sites were used to measure the free-fall acceleration of g. Each gravimeter measured the value of g at a subset of three of the sites, for a total set of 27 g-values for the comparison. The absolute gravimeters agree with one another with a standard deviation of 1.6?μGal (1 Gal ≡ 1?cm s ^?2). The minimum and maximum offsets are ?2.8 and 2.7?μGal. This is an excellent agreement and can be attributed to multiple factors, including gravimeters that were in good working order, good operators, a quiet observatory, and a short duration time for the experiment. These results can be used to standardize gravity surveys internationally.  相似文献   

A conceptual template for integrative human–environment research     

Barry Newell  Carole L. Crumley  Nordin Hassan  Eric F. Lambin  Claudia Pahl-Wostl  Arild Underdal  Robert Wasson   《Global Environmental Change》2005,15(4):299-307

Knowledge integration, the blending of concepts from two or more disciplines to create innovative new worldviews, is a key process in attempts to increase the sustainability of human activities on Earth. In this paper, we describe a ‘conceptual template’ that can be used to catalyse this process. The template comprises (a) a list of high-level concepts that capture the essential aspects of any significant human–environment problem, plus (b) broad lists of low-level basic concepts drawn from a range of disciplines. Our high-level concepts, which we call ‘conceptual clusters’, are labelled Dynamics & System, Organisation & Scale, Controlling Models, Management & Policy, Adaptation & Learning, and History. Many of the clustered, lower-level concepts are synonyms and thus provide possible connections between disciplines—for this reason we call them ‘nexus concepts’. We suggest that a conceptual template like that presented here can provide strong support to the initial phases of integrative research programs.  相似文献